Some electronic apparatuses are provided with a cover to protect a part of an apparatus, e.g. a console, or a control panel. An example of such apparatus is a power supply apparatus for arc welding machines with a cover attached to it, disclosed in Catalogue No. 291W71 DITJ-0400-0.3 (TD) 285 for a full-digital inverter TIG welder “SANARG ID/IA Series” manufactured by Sansha Electric Manufacturing Company, Limited. As shown in FIG. 1, this power supply apparatus includes a generally box-shaped housing 1, and a console 2 generally rectangular in shape is mounted to an upper front portion of the housing 1. Although not shown, a plurality of controls and indicators are operatively disposed on the console 1, including a jog dial 3 acting as a multi-functional control. A generally rectangular cover 4 is adapted to cover the entire surface of the console 2.
As indicated by an arrow 5 in FIG. 1, the cover 4 can rotate about an axis located near the upper edge of the cover 4. When a control on the console 2 is to be operated, the cover 4 is rotated upward to a position indicated by broken lines 4a. Since the jog dial 3 is operated more frequently than other controls, it is so arranged so as to be operated through a through-hole 6 in the cover 4 even when the cover 4 is in its closed position.
As shown in FIGS. 2A and 2C, the cover 4 has a generally flat main section 42. Two side walls 44 extend along right and left side edges of the main section 42 in such a manner as to face each other. Top and bottom walls 46 and 48 are formed respectively along the upper and lower edges of the main section 42. The main section 42 is adapted to overlie the console 2. The through-hole 4 is formed in a relatively lower portion of the main section 42. The lower portion of the main section 42 including the through-hole 6 is set back toward the housing 1 (FIG. 1) so that a relatively large portion of the jog dial 3 can protrude out through the through-hole 6, facilitating easy operation of the jog dial 3.
The opposing side walls 44 are perpendicular to the main section 42 and extend backward, i.e. toward the housing 1. Each of the side walls 44 includes a thick disc-shaped portion 50 disposed on the extension of the upper edge of the main section 42. A retainer, e.g. a short columnar protrusion 52, is formed to extend outward from the center of each disc-shaped portion 50 along the extension of the upper edge of the main section 42. The upper portions 54 of the side walls 44 including the protrusions 52 can be elastically deformed when external force is exerted to them in the inward direction as indicated by arrows 100 in FIGS. 2A and 2C. For that purpose, slits 56 are formed to extend from the opposite ends of the upper edge of the main section 42 to locations somewhat below the respective disc-shaped portions 50.
An upper wall 46 extends backward from the upper edge of the main section 42 at an obtuse angle larger by 10 degrees than right angles. The slits 56 formed in the main section 42 extend into the upper wall 46 so that they are located between the respective side walls 44 and the upper portions 54 of the main section 42.
The lower wall 48, too, is at an obtuse angle larger by about 10 degrees than right angles with respect to the main section 42, but it extends forward, i.e. away from the housing 1. The front surface of the console 2 covered by the main section 42 faces diagonally upward at an angle of about 10 degrees with respect to the vertical plane, and the lower and upper walls 48 and 46 are at an obtuse angle with respect to the main section 42, so that the lower and upper walls 48 and 46 can assume the horizontal position when the cover 4 is placed over the console 2.
The cover 4 is formed of a synthetic resin, e.g. polycarbonate resin, and is formed as a single member. The width of the main section 42 is dependent on the size of the housing to which the cover 4 is to be mounted, but it may be, for example, about 150 mm. The height may be about 120 mm. The backward dimension of the main section 42, i.e. the distance between the foremost and rearmost edges of each of the side walls 44, does not exceed about 15 mm, and the forward dimension, i.e. distance over which the lower wall 48 extends, is about 12 mm. The thickness of the cover 4 is about 3 mm over its entirety. The length of the slits 56 is about 20 mm, and the width is about 2 mm. The length of the protrusions 52 is also about 2 mm.
When the cover 4 is attached to the housing 1, the upper elastic portions 54 of the side walls 44 including the protrusions 52 are bent inward as indicated by arrows 100 in FIG. 3 by, for example, an assemblyman. Then, the entire cover 4 is placed in position with respect to the housing 1, e.g. into the space between opposing two side walls 1a of the housing 1, where the protrusions 52 are in alignment with associated holes 7 respectively formed in the side walls 1a of the housing 1. The elastic portions 54 are then released so that the protrusions 52 can fit into the associated holes 7 by virtue of the elastic restoration of the elastic portions 54, as shown in FIG. 4. Thus, the cover 4 is mounted to the housing 1 in such a manner as to be able to rotate about an axis passing through the protrusions 52.
In order for the respective protrusions 52 to be fitted into the holes 7 through the elastic deformation of the elastic portions 54 including the protrusions 52, the distance between the openings of the opposing holes 7 should be larger than the distance between the tip ends of the protrusions 52 when they are elastically bent inward, smaller than the distance between the tip ends of the protrusions 52 when they elastically restore their original position, and larger than the distance between the proximal ends of the protrusions 52 when they are in their restored position. Furthermore, the depth of each hole 7 should be larger than the length of the associated one of the protrusions 52.
If the cover 4 is pulled forward or upward with a strong force, the elastic portions 54 including the protrusions 52 may sometimes be elastically deformed to cause the protrusions 52 to slip off from the holes 7, resulting in disengagement or falling-off of the cover 4 from the housing 1. Repetitive disengagement of the cover 4 will then cause reduction of the mechanical strength of the elastic portions 54, possibly leading to ultimate breakage of the elastic portions 54.
An object of the present invention, therefore, is to provide an attachment for preventing a cover attached to a housing from falling off to thereby prevent the cover from being broken.